Process and apparatus for melting slag

ABSTRACT

A process and an apparatus for melting rock, slag, glass or other similar material or combination thereof for use in the production of high quality mineral wool fibers is disclosed. The apparatus includes a cupola to which is charged a base support of high temperature lump refractory material to serve as a permeable support for the slag charge. Gas-fired burners located along the side walls of the cupola below the upper level of the bed of lump refractory material produce hot combustion gases which move through the refractory bed and upward through the slag, melting it in the lower regions and preheating it in the upper part of the cupola. A water-cooled notch can be located at the bottom of the cupola to allow a pool of molten slag to accumulate, so that particles of unmelted slag which reach the bottom of the cupola will melt prior to being discharged from the cupola. The lump refractory material is selected for its high temperature and high load-bearing properties.

United States Patent Richardson et al.

3,658,307 51 Apr. 25, 1972 Primary Examiner-John J. CambyAttorney-Martha L. Ross [54] PROCESS AND APPARATUS FOR MELTING SLAGABSTRACT paratus for melting rock al or combination thereof slag, glassor both of A process and an ap other similar materi for use in theproduction of high quality mineral wool fibers is disclosed. Theapparatus includes a cupola to which is cha [73] Assignee: TheSusquehanna Corporation, Fairfax County, Va.

rged a base support of high temperature lump refractory material toserve as a permeable support for the slag charge. as-fired burnerslocated along the side walls of the cu level of the bed of lumprefractor [22] Filed: Aug. 4, I970 pola below the upper y materialproduce hot com- 21 Appl.No.: 60,893

h the refractory bed and upmelting it in the lower regions and prer partof the cupola. A water-cooled at the bottom of the cupola to allow a g uo r h t e m e mg ape C m 6 C womb h e wwFmb a In m a nm .m .mh fl aw U60 bwhn 92 2 205 WW .m ,N 7 m a w 2 zwm "l b 7 .2 MI

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o accumulate, so that particles of unach the bottom of the cupola willmelt e ncdbr m nM mw n my w I." we Pm M C s m N m R l. 6 5

prior to being discharged from the cupola. The lump refracto ry materialis selecte bearing properties.

UNITED STATES PATENTS d for its high temperature and high load- 263/27 X..t.263 /29 X 2,161,180 6/1939 Marx 2,521,830 9/1950Collins...............

15 Claims, 2 Drawing Figures u on PROCESS AND APPARATUS FOR MELTING SLAGBACKGROUND AND SUMMARY OF THE INVENTION This invention relates to aprocess and apparatus for melting slag or other mineral wool producingmaterial. More particularly, this invention relates to a gas-firedcupola and a method of melting slag using the cupola which contains apermeable support of high temperature, high load-bearing lump refractorymaterial, through which combustion gases move to melt the slag which issupported on the refractory material so that the slag flows down throughthe refractory material and out of the cupola at its lower end in auniform molten form, suitable for spinning into high quality mineralwool fibers.

The production of mineral fibers, such as mineral wool, requires themelting of the raw material which is rock, slag, glass or other similarmaterial or combination thereof prior to forming such materials into themineral fibers. Typical prior an apparatus for the melting of suchmaterials has included water cooled metal cupolas in which the raw slagmaterial is heated in the presence of air and a suitable fuel such ascoke. The cupola is generally charged in alternate layers of coke andslag. In such prior art cupolas, the coke is frequently used not only asa source of fuel but also as a support for the slag charge. Suchcoke-fired cupolas are expensive to operate, due to the relatively highcost of coke, and the mineral wool fibers made from slag produced insuch cupolas is often of inferior quality due to the high carbon contentof such slag.

By the present invention, there is provided an efficient process for theproduction of a uniform molten slag suitable for forming into mineralwool fibers of high quality. The term slag" is used herein and in theclaims to describe any of the various raw mineral materials, such asrock, slag, glass or other similar well-known materials, used in theproduction of mineral wool and other mineral fibers. The presentinvention involves the use of a gas-fired cupola in conjunction with abed of high temperature, high loadbearing lump refractory material toproduce a uniform molten slag, suitable for forming mineral wool fibersof high quality. A permeable bed of the lump refractory material is laiddown at the bottom of the eupola to provide a permeable support for theslag charge. Gas burners are situated around the lower extremity of thecupola and open directly into the refractory bed. The upper level of thebed of refractory material extends above the gas burners with the resultthat a uniform high temperature can be achieved throughout therefractory bed. The particular refractory bed temperature employed willdepend on the nature of the raw materials which are being reduced to themelted form. Typical temperatures employed include a range of about2,500 to 3,000 F. The hot combustion gases produced by the gas burnersmove upward from the refractory bed through the slag, melting the slagin the lower regions and preheating it in the upper part of the cupola.In heating the slag sufiiciently to allow it to flow in a molten form,much of the heat transfer to the slag takes place within the refractorybed. Thus sufficient heat is provided to cause the slag located at theinterface with the refractory bed to begin to flow down through the bed.As the slag moves downward through the bed, additional heat is added toproduce a molten slag having the desired low viscosity for spinning. Asthe slag melts, it moves downward through the refractory bed andcollects at the bottom of the cupola. A water-cooled notch located inthe inner base of the cupola is provided for discharge of the moltenslag from the cupola. The opening in the discharge notch is situatedabove the bottom of the cupola to allow a pool of molten slag toaccumulate priorto discharge, so that any particles of unmelted slagwhich reach the bottom of the cupola will melt prior to being dischargedfrom the cupola. By using gas as a fuel rather than coke, the carboncontent of the slag can be held to a minimum, thus improving the qualityof the fiber. The use of gas also results in a less expensive operationas well as a reduction in the emission of air pollutan Referring now tothe drawings:

FIG. 1 is a vertical section of a cupola constructed according to theprinciples of the present invention;

FIG. 2 is a perspective view with cut-away section of the water-cooleddischarge notch which is mounted in the bottom of the cupola to providefor discharge of the molten slag.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment of thepresent invention as shown in FIG. 1, apparatus 10 is provided formelting slag which includes a water-cooled cupola 11 having a waterinlet 12 at the bottom and a water outlet 13 at the top of the cupola. Acupola of any convenient size may be employed; a cupola having an innerdiameter of 5 feet has been used with good results. The cupola has anouter shell 14 and an inner shell 15, each shell being made of steel orother similar material, with space between for the circulation of water.A charging hood 2! located above and connected to the upper part of thecupola 11 provides a storage area for the preheating of the raw slagmaterial. The hood also serves as a discharge duct for the products ofcombustion. The charging hood 21 is connected to a stack 22 through aconical section 23. A skip bucket 24 delivers the refractory supportmaterial 36 and raw slag material 27 to the charging magazine 25 locatedwithin the charging hood 21. The charging hood 21 is lined withrefractory material 26. Heavy duty hinged doors 31 of steel or a similarmaterial are located at the lower end of the cupola. These doors are soconstructed as to allow the cupola to be emptied of lump refractorysupport material and slag at the end ofan operating period. Gas burners32 are provided along the sidewalls around the circumference of thecupola. Gas lines 33 are provided to deliver gas at preset pressure andvolume to the gas burner mixing housings 34 while combustion air ducts3S deliver air to the gas burner mixing housings. The cupola is filledto a level above the uppermost gas burners, as for example, to a levelabout 6 to 8 inches above the upper row of gas burners 32 with a hightemperature, high load-bearing, lump refractory material 36 so that thehot combustion gases are introduced directly into the refractory bed. Anexample of such a material is the aluminum oxide refractory bed supportsold by The Carborundum Company having a lump size of 2 to 3 inches, amelting point of approximately 3,700 F. and with the following analysis:

Al O (by difference) 99.53% SiO, 0.04% I-e,0 0.10% Na,0 0.33%

The refractory material should have a lump size which will allowcombustion gases and the molten slag to move through the refractory bedwhile the size should be small enough to prevent the unmelted slag fromfalling through the bed. A refractory material having a lump size ofabout 1 to 4 inches is often employed. The refractory material shouldalso be able to support heavy slag loads while being subjected to thehigh temperatures which are employed within the refractory bed.Typically, a bed of the refractory material should be able to support aload of at least about 10,000 pounds while heated to temperatures in therange of 2,500 to 3,000" P. The gas burners 32 provided along the lowerside wall of the cupola are situated so as to open directly into therefractory support bed 36. A water-cooled steel discharge notch 37 islocated in the bottom of cupola l1 and is provided with a dischargeopening 43 which allows the molten slag 38 to be continuously dischargedfrom the cupola as the slag is melted. This watercooled discharge notch37 is also shown in a perspective view in FIG. 2. The discharge notch 37is provided with an inlet line 40 and an outlet line 41 for coolingwater. A layer of carborundum bricks or other high temperaturerefractory material 42 is closely laid over the lower cupola doors 31 asa protective covering for the bottom of the cupola to withstand the hightemperature of the molten slag.

In operation, the lower doors 31 are closed and locked in position and alayer of refractory material 42 laid over the doors. The watercirculating system is put into operation and the water cooled notch 37is then placed and locked in position. The refractory support material36 is then introduced into the cupola by the skip hoist bucket 24.Sufiicient refractory material is delivered to fill the bottom sectionof the eupola 11 to a height above that of the upper row of gas burners32, for example, to about 6 to 8 inches above the uppermost burners. Thelower row of burners are then fired one at a time until the entire lowerrow of burners have been ignited. After the lower row of gas burners hasburned for approximately one-half hour, the upper row of burners isignited and the refractory support material 36 is then heated forapproximately 2 hours until a temperature of, for example, about 2,5003,000 F. is achieved throughout the support material. When thistemperature has been reached, the raw slag material 27 is thenintroduced into the cupola. During the initial heat-up period, theproducts of combustion have been discharging through the charging hood21 and the charging magazine 25 and out through the stack 22. The rawslag material 27 is delivered to the cupola by the skip hoist bucket 24.The slag passes through the charging magazine 25 and comes to rest ontop of the refractory support bed 36. Charging continues until thecupola 11 and the charging magazine 25 are filled. The heat generatedwithin the refractory bed 36 by the gas burners 32 melts the raw slag 27adjacent to the refractory bed and preheats the slag 27 in the upperpart of the cupola 11 and in the charging magazine 25. The hotcombustion gases produced by the gas burners pass through thewater-cooled cupola section 11 and some of the gas continues up throughthe charging magazine 25 while the balance discharges through the spacesurrounding the charging magazine and out through the stack 22. Thedischarge opening 43 in the water cooled notch 37 is preferably situatedseveral inches, for example, about 4 to 6 inches above the refractorybottom 42 of the cupola 11 to allow a pool of molten slag to accumulatein the bottom of the cupola 11 prior to the initial flowing of themolten slag 38 out of the cupola. In this manner, any small particles ofunmelted slag which reach the slag pool will melt in the pool and mixwith the other molten slag prior to discharging from the cupola. The rawslag material 27 can be charged continuously to the cupola 11 and themolten slag 38 will flow continuously from the cupola as long as theburners 32 deliver sufficient heat.

From the foregoing description, it is apparent that the apparatus of thepresent invention can be installed in cupolas presently in operation toprovide a uniform molten slag of high quality. Additional advantagesinclude the elimination of coke, and the substitution of the muchcheaper gas fuel with the resulting lower end cost of the productproduced. In addition, material handling costs are reduced. Theelimination of coke also reduces pollution emission, with anaccompanying reduction in the cost of air pollution correctiveequipment.

It is thought that the invention and many of its attendant advantageswill be understood from the foregoing description, and it will beapparent that various changes may be made in the form, construction andarrangement of the parts without departing from the spirit and scope ofthe invention or sacrificing its material advantages, the formshereinbefore described being merely preferred embodiments thereof.

It is claimed:

1. A process for melting slag which comprises:

a. charging a cupola having gas heating means with a lump refractorymaterial to form a refractory bed having an upper level above that ofthe gas heating means, said refractory material having a melting pointabove that of the slag to be melted,

b. heating the lump refractory material by directly injecting thecombustion gases of the gas heating means into the refractory bed mass,

0. charging slag to the cupola, whereby said slag rests on saidrefractory material,

d. passing heat from the heated bed of refractory material into the slagto melt it so that the slag flows through and is further heated in thebed of refractory material, and

e. withdrawing the melted slag from the bed of refractory material.

2. The process of claim 1 in which the gas heating means comprises atleast one row of gas burners arranged around the lower extremity of thecupola and opening directly into the lump refractory material within thecupola.

3. The process of claim 2 in which the lump refractory material ischarged to a level about 6 to 8 inches above the level of the gasheating means. I

4. The process of claim 3 in which the lump refractory materialcomprises an aluminum oxide support having a lump size of about I to 4inches.

5. The process of claim 3 in which the lump refractory material isheated to a temperature in the range of about 2,500 to 3,000 F.

6. The process of claim 1 including means for accumulating the meltedslag in the bottom ofthe cupola.

7. Apparatus for melting slag which comprises:

a. a refractory chamber,

b. a high load-bearing, lump refractory material filling said refractorychamber, said refractory material having a melting point above that ofthe slag to be melted,

c. gas means for providing heat to the refractory chamber, said gasmeans being located below the upper level of the refractory chamber andpositioned to inject its combustion gases directly into the refractorymaterial mass,

d. a chamber located above the refractory chamber, communicating withthe refractory chamber and adapted to be filled with slag, and

e. an opening for the discharge of melted slag.

8. The apparatus of claim 7 in which the gas means comprises at leastone row of gas burners arranged around the lower extremity of therefractory chamber and opening directly into the interior of therefractory chamber.

9. The apparatus of claim 8 including means for accumulating the meltedslag in the bottom of the refractory chamber.

10. A process for melting slag in a cupola where said cupola is providedwith a plurality of gas burners at the lower portion thereof,comprising:

a. charging said cupola with a lump refractory material to form apermeable bed of refractory material, the upper level of said bed lyingabove that of said gas burners, said refractory material having amelting point above that of the slag to be melted,

b. heating said bed by injecting the hot combustion gases from saidburners directly into the refractory bed mass to provide a temperaturelevel in said bed sufficient to melt slag,

c. charging slag to said cupola whereby said slag rests on said bed ofrefractory material,

d. passing heat from said bed to said slag to initiate flowing of saidslag into said bed,

e. heating said slag while in said bed into a molten state, and

f. withdrawing the melted slag from said bed.

11. A process as claimed in claim 10 wherein the step of heating saidbed elevates the temperature of said bed to the range ofabout 2,500 to3,000 F.

12. A process as claimed in claim 11 wherein the step of charging saidcupola with lump refractory material results in an upper bed level atleast 6 inches above said gas burners.

13. A cupola for the melting of slag comprising:

a. a refractory chamber,

b. a permeable bed of lump refractory material filling said refractorychamber, said refractory material having a melting point above that ofthe slag to be melted,

c. a second chamber for retaining the slag to be melted, said secondchamber being positioned upstream of said refractory chamber and incommunication therewith,

d. means for providing gas-fuel-fired heat directly into said refractorychamber, said means being spaced about and opening into said refractorybed to inject its combustion gases directly into the refractory materialmass, whereby said means will heat said bed to a level sufficient tomelt slag, and

e. an opening in said refractory chamber for the discharge of meltedslag.

14. A cupola as claimed in 13 wherein said providing means includes aplurality of gas burners spaced'about and opening directly into saidrefractory bed.

15. A cupola as claimed in claim 14 further comprising: a. a charge ofslag in said second chamber, 5 b. said bed of lump refractory materialserving as a support bed for said slag.

2. The process of claim 1 in which the gas heating means comprises atleast one row of gas burners arranged around the lower extremity of thecupola and opening directly into the lump refractory material within thecupola.
 3. The process of claim 2 in which the lump refractory materialis charged to a level about 6 to 8 inches above the level of the gasheating means.
 4. The process of claim 3 in which the lump refractorymaterial comprises an aluminum oxide support having a lump size of about1 to 4 inches.
 5. The process of claim 3 in which the lump refractorymaterial is heated to a temperature in the range of about 2,500* to 3,000* F.
 6. The process of claim 1 including means for accumulating themelted slag in the bottom of the cupola.
 7. Apparatus for melting slagwhich comprises: a. a refractory chamber, b. a high load-bearing, lumprefractory material filling said refractory chamber, said refractorymaterial having a melting point above that of the slag to be melted, c.gas means for providing heat to the refractory chamber, said gas meansbeing located below the upper level of the refractory chamber andpositioned to inject its combustion gases directly into the refractorymaterial mass, d. a chamber located above the refractory chamber,communicating with the refractory chamber and adapted to be filled withslag, and e. an opening for the discharge of melted slag.
 8. Theapparatus of claim 7 in which the gas means comprises at least one rowof gas burners arranged Around the lower extremity of the refractorychamber and opening directly into the interior of the refractorychamber.
 9. The apparatus of claim 8 including means for accumulatingthe melted slag in the bottom of the refractory chamber.
 10. A processfor melting slag in a cupola where said cupola is provided with aplurality of gas burners at the lower portion thereof, comprising: a.charging said cupola with a lump refractory material to form a permeablebed of refractory material, the upper level of said bed lying above thatof said gas burners, said refractory material having a melting pointabove that of the slag to be melted, b. heating said bed by injectingthe hot combustion gases from said burners directly into the refractorybed mass to provide a temperature level in said bed sufficient to meltslag, c. charging slag to said cupola whereby said slag rests on saidbed of refractory material, d. passing heat from said bed to said slagto initiate flowing of said slag into said bed, e. heating said slagwhile in said bed into a molten state, and f. withdrawing the meltedslag from said bed.
 11. A process as claimed in claim 10 wherein thestep of heating said bed elevates the temperature of said bed to therange of about 2,500* to 3,000* F.
 12. A process as claimed in claim 11wherein the step of charging said cupola with lump refractory materialresults in an upper bed level at least 6 inches above said gas burners.13. A cupola for the melting of slag comprising: a. a refractorychamber, b. a permeable bed of lump refractory material filling saidrefractory chamber, said refractory material having a melting pointabove that of the slag to be melted, c. a second chamber for retainingthe slag to be melted, said second chamber being positioned upstream ofsaid refractory chamber and in communication therewith, d. means forproviding gas-fuel-fired heat directly into said refractory chamber,said means being spaced about and opening into said refractory bed toinject its combustion gases directly into the refractory material mass,whereby said means will heat said bed to a level sufficient to meltslag, and e. an opening in said refractory chamber for the discharge ofmelted slag.
 14. A cupola as claimed in 13 wherein said providing meansincludes a plurality of gas burners spaced about and opening directlyinto said refractory bed.
 15. A cupola as claimed in claim 14 furthercomprising: a. a charge of slag in said second chamber, b. said bed oflump refractory material serving as a support bed for said slag.